The invention relates to a semiconductor component having a semiconductor body of a first conductivity type. A semiconductor region of the first conductivity type is provided between two electrodes and can sustain a reverse voltage applied to the electrodes. Semiconductor regions of a second conductivity type, opposite to the first conductivity type, are provided in at least one plane extending essentially perpendicularly to a connecting line between the two electrodes. A cell array is disposed below one of the electrodes in the semiconductor body.
Unipolar power semiconductor components for high reverse voltages have a high on resistance due to the required low doping concentration of the semiconductor region that takes up the space charge zone. If the doping concentration is increased in this semiconductor region, then the blocking capability of the power semiconductor component decreases.
In order to solve this problem, additional, buried pn junctions can be produced in the bulk of the semiconductor region that takes up the reverse voltage. European Patent No. EP 0 344 514 B1 has already proposed a turn-off thyristor in which there is inserted into a base layer, which is not contact-connected by a gate electrode, at least one thin semiconductor layer which is not connected up to external a potentials and is doped oppositely relative to the base layer. Instead of such a non-contact-connected layer, at the present time preferably laterally uniformly distributed spherical semiconductor regions, which, if appropriate, can also form a network, are introduced into the semiconductor region that takes up the space charge zone, the semiconductor regions, having a conductivity type opposite to the conductivity type of the semiconductor region. The semiconductor regions are preferably floating. With a configuration of this type, the maximum electric field strength that occurs is limited depending on the basic doping in the semiconductor region and the distance between the electrically floating regions of the opposite conductivity type to the conductivity type of the semiconductor region.
International Publication No. WO 97/29518 describes a power semiconductor component according to the principle of charge carrier compensation. In that case, the drift zone of the semiconductor component has regions of different conductivity types, the total quantity of charge carriers of different conductivity types being approximately the same in these regions. When a reverse voltage is applied, the regions are mutually depleted, with the result that the semiconductor component exhibits an improved blocking capability. By virtue of the fact that the drift zone simultaneously has a higher doping concentration, the on resistance Ron is significantly reduced in the case of such a semiconductor component.
The fabrication of, for example, p-conducting semiconductor regions in an n-conducting semiconductor region can be effected through the use of a multistage epitaxy, in association with a phototechnology and a subsequent ion implantation.
If, in the semiconductor body of a semiconductor component, a plurality of such semiconductor regions of the second conductivity type which are provided essentially parallel to one another in different planes are cascaded in a semiconductor region of the first conductivity type, so that there are thus p-doped floating semiconductor regions, for example, in an n-conducting semiconductor region xe2x80x94which takes up the space charge zone xe2x80x94in different planes perpendicular to the connection direction between source electrode and drain electrode, then high reverse voltages in conjunction with a low on resistance Ran can be achieved with a semiconductor component of this type. In this way, it is thus possible to fabricate, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) with a high reverse voltage together with a low on resistance Ron.
One disadvantage of electrically floating semiconductor regions of the second conductivity type in a semiconductor region xe2x80x94which takes up or accommodates the space charge zone xe2x80x94of the first conductivity type can be seen, however, in the fact that, especially in unipolar semiconductor components, the floating semiconductor regions delay switching operations: such slow switching operations are caused by the lack of coupling of the semiconductor regions of the second conductivity type to the source electrode or cathode, for example, via a unipolar conduction path.
It is accordingly an object of the invention to provide a semiconductor component for high reverse voltages in conjunction with a low on resistance which overcomes the above-mentioned disadvantages of the heretofore-known semiconductor components of this general type and in which switching operations proceed rapidly. It is a further object of the invention to provide a method for fabricating such a semiconductor component.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor component, including:
two electrodes;
a semiconductor body of a first conductivity type, the semiconductor body including a semiconductor region of the first conductivity type provided between the two electrodes, the semiconductor region of the first conductivity type being configured to sustain a reverse voltage applied to the electrodes;
semiconductor regions of a second conductivity type disposed in at least one plane extending essentially perpendicularly to a connecting line extending between the two electrodes, the second conductivity type being opposite to the first conductivity type;
a cell array disposed under one of the electrodes in the semiconductor body; filiform semiconductor zones of the second conductivity type; and
at least some of the semiconductor regions of the second conductivity type being connected to the cell array via the filiform semiconductor zones of the second conductivity type.
In other words, a semiconductor component according to the invention includes a semiconductor body of the first conductivity type, in which a semiconductor region of the first conduction type is provided between two electrodes, which region takes up a reverse voltage (blocking voltage) applied to the electrodes and in which region semiconductor regions of the second conductivity type, opposite to the first conductivity type, are provided in at least one plane extending essentially perpendicularly to the connecting line between the two electrodes, and in which a cell array is situated below one of the electrodes in the semiconductor body, wherein the semiconductor regions of the second conduction type are connected to the cell array at least partly via filiform semiconductor zones of the second conduction type.
In the case of a semiconductor component of the type mentioned above, the object of the invention is achieved according to the invention by virtue of the fact that the semiconductor regions of the second conductivity type are connected to the cell array at least partly via the filiform semiconductor zones of the second conductivity type, which are doped more weakly than the semiconductor regions of the second conductivity type.
According to another feature of the invention, the filiform semiconductor zones have a cross-sectional configuration, of a cylinder, a cross-sectional configuration of a parallelepiped or a cross-sectional configuration of a strip.
According to yet another feature of the invention, the semiconductor body has an edge region; and given ones of the semiconductor regions of the second conductivity type are disposed in the edge region of the semiconductor body and are configured as floating semiconductor regions. For edge structures, it is expedient here for not all the semiconductor regions of the second conductivity type to be connected to the source electrode via the filiform zones of the second conductivity type. Rather, it is advantageous if floating semiconductor regions of the second conductivity type are present in the edge structure, the regions not being connected to the source electrode via the filiform zones.
According to another feature of the invention, the semiconductor region of the first conductivity type have, relatively more weakly doped zones and relatively more heavily doped zones extending in a direction between two electrodes such that the semiconductor regions of the second conductivity type are provided in the relatively more weakly doped zones, and such that the relatively more heavily doped zones extend in the semiconductor body substantially below the gate electrodes.
According to a further feature of the invention, the semiconductor region of the first conductivity type has a first dopant concentration; and doped zones of the first conductivity type are incorporated into the semiconductor is region of the first conductivity type, the doped zones have a second dopant concentration greater than the first dopant concentration.
According to yet another feature of the invention, the semiconductor region of the first conductivity type includes surface zones disposed below the gate electrodes and doped more heavily than a remainder of the semiconductor region of the first conductivity type.
According to a further feature of the invention, the filiform semiconductor zones have a dopant concentration of less than 1016 charge carriers cmxe2x88x923.
According to another feature of the invention, each of the filiform semiconductor zones has a center, an outer edge and a total charge integrated from the outer edge to the center, the filiform semiconductor zones are configured such that the total charge is less than a breakdown charge.
According to yet a further feature of the invention, the filiform semiconductor zones are doped more weakly than the semiconductor regions of the second conductivity type.
With the objects of the invention in view there is also provided, a method for fabricating a semiconductor component, the method includes the steps of:
providing a semiconductor body having a semiconductor region of a first conductivity type;
etching holes into the semiconductor region of the first conductivity type;
subsequently implanting dopants of a second conductivity type opposite the first conductivity type at a bottom of each of the holes;
producing semiconductor regions of the second conductivity type by driving the dopants into the semiconductor region of the first conductivity type;
subsequently extending the holes deeper into the semiconductor region of the first conductivity type by performing an anisotropic etching;
subsequently implanting dopants of the second conductivity type at the bottom of each of the holes; and
connecting at least some of the semiconductor regions of the second conductivity type toga cell array disposed in the semiconductor body via filiform semiconductor zones of the second conductivity type.
With the objects of the invention in view there is further provided, a method for fabricating a semiconductor component, the method includes the steps of:
providing a semiconductor body of a first conductivity types the semiconductor body including a semiconductor region of the first conductivity type;
providing semiconductor regions of a second conductivity type disposed in at least one plane extending essentially perpendicularly to a connecting line extending between two electrodes, the second conductivity type being opposite the first conductivity type;
providing a cell array disposed under one of the electrodes in the semiconductor body;
fabricating filiform semiconductor zones of the second semiconductor type by introducing trenches into the semiconductor region of the first conductivity type as far as the semiconductor regions of the second conductivity type by providing the trenches with zones of the second conductivity type in side walls of the trenches, and by filling the trenches with an insulating material; and
connecting, via the filiform semiconductor zones of the second conductivity type, at least some of the semiconductor regions of the second conductivity type to a cell array disposed in the semiconductor body.
With the objects of the invention in view there is also provided, a method for fabricating a semiconductor component, the method includes the steps of:
providing a semiconductor body of a first conductivity type, the semiconductor body including a semiconductor region of the first conductivity type;
providing semiconductor regions of a second conductivity type disposed in at least one plane extending essentially perpendicularly to a connecting line extending between two electrodes, the second conductivity type being opposite the first conductivity type;
fabricating filiform semiconductor zones of the second semiconductor type by introducing holes into the semiconductor region of the first conductivity type such that the holes have a respective cross section tapering conically toward a hole bottom; and
connecting, via the filiform semiconductor zones of the second conductivity type, at least some of the semiconductor regions of the second conductivity type to a cell array disposed in the semiconductor body.
In other words, in a method for fabricating the semiconductor component according to the invention, a hole is introduced into the semiconductor region of the first conductivity type by anisotropic etching. Boron, for example, is subsequently implanted into the hole, in the bottom thereof. After a brief drive-out of the dopant, further anisotropic etching is then effected, and then implantation is again effected into the bottom of the hole. This sequence can be repeated until the desired number of planes with semiconductor regions of the second conductivity type has been produced. Finally, after the last doping of the hole bottom, the hole is filled with dopant by epitaxy. Instead of such in-situ-doped epitaxy, however, it is also possible to fill the holes with insulating material, such as silicon dioxide for example. This can be done when the filiform zone of the second conductivity type runs in the edge of a hole, for example, which can be done by ion implantation into hole walls that taper somewhat obliquely downward. In this case, there is a high doping concentration with much boron, for example, at the bottom of a hole, while the side walls thereof are only weakly doped with boron. This weak doping suffices, however, to connect the individual semiconductor regions, which are p-doped in the present example, to the source electrode in a unipolar manner.
Thus, in the case of the semiconductor component according to the invention, filiform, weakly doped zones of the second conductivity type with a doping concentration of, for example, less than 1016 charge carriers cmxe2x88x923 are provided as xe2x80x9cconnection cylinderxe2x80x9d or xe2x80x9cconnection parallelepipedxe2x80x9d between the highly doped semiconductor regions of the second conductivity type. As a result, the otherwise electrically floating semiconductor regions of the second conductivity type are resistively connected to the cell array or to the source.
When a voltage is applied to source and drain, in the case of in the semiconductor component according to the invention, firstly the n-conducting semiconductor region is depleted simultaneously via all the p-conducting semiconductor regions that are connected to one another by doping threads.
The interspace between the semiconductor regions of the second conductivity type is thus depleted of free charge carriers, in order to produce the space charge zone there, which can take up an electrical voltage. If, in the filiform semiconductor zones of the second conductivity type, the total charge, integrated from the outer edge of the filiform zone as far as the center thereof, is less than the breakdown charge, which is related to the breakdown voltage by Maxwell""s third equation, the filiform zone is completely depleted, so that the space charge zone can be built up for taking up the electrical voltage.
In other words, in the case of the semiconductor component according to the invention, the filiform zone thus connects all the semiconductor regions of the second conductivity type to the source electrode via a resistive path, without impeding the buildup of a space charge zone.
The filiform zones of the second conductivity type which connect the semiconductor regions of the second conductivity type to one another enable the semiconductor regions of the second conductivity type to be rapidly discharged after a switch-on. In other words, the switch-on operation is significantly accelerated.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor component for high reverse voltages in conjunction with a low on resistance and method for fabricating such a semiconductor component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.